Method and apparatus for testing wire



10, P. c CLARKE' METHOD AND APPARATUS FOR TESTING WIRE Filed Aug. 16,1944

Patented Feb. 10, 1948 1,435,712 QMETHODANDJAPPARATU FOR TESTING Phiilp momma-"me" Lexington, Pan, asslgnorito "'Hmiter'i'neswd i Stee'l Company, Lansdal zn-lenrporatinn rnfiifiennsylvania ili ,ihpplicatlonflugustjlfi, 1944,. Serla1 No. 549,741

:ll'ClaimS.

This mvention reiates to a "method and apparatus for testing wireand, more particularly, relates to r-netl'rod and apparatus iior subjecting wiretoarotsiting'beam taitlguetest.

'IIhe method accordingtothis invention will f lberio'undlto :be highly accurate, end-nut "the same according to this inventioniwill he 'ioundsmost adaptable for the readyiand accurate itatigue testing of small diameter Wire, as, for example, wire :o :a, diameter within =say about the range -'=o.-coi-o;-1 inch,1though,as "appear, wire or a diameter in excess "of on men may be readily tested where sulficient space is available.

Having now indicated, in a general way, the mature and purposef the method and apparatus according to this invention, I will proceed to s, detailed description thereof with reference to .the'accompanying drawtng' inwhfich:

Figure 1 a perspective view "showingthe es- *sential elements of a simple "form 'of apparatus according tofliisinventlon.

Figure 2 is a-diagram'ma't-ic view illustrating the set-up of wire to lbeitested according to the method of this invention.

Figure 3 illustrates an electrical circuit adapted for .embodiment..;in apparatus shown Figrel.

' Figure 4 is 'a view part'ly insection, showing .a detailof construction.

Beferring now more particularly to Figures 1 and hair ine C. .or I). C motor 1 isimou-nted one. table 2, ,or otherlsu-itableisupl iflnt. Mounted .an endportion of a wire 4 tobe tested.

lAdjacent to the motor -I and extending :at right angles to the axis ref theamotor shaft, is we ,rectangularmetaltbarfi. The-the r fiisrsu-pported from ;-the table 12 by -means of :lmacleets B,, and the baris provided with ,atserleswfdrilled-holes J, J aforthe-zreoeption not an end portion .-of the wire 4. Theiholes 5|, 3| arespaced nbo ve the sur- --f-ace of table a at rt-hexsame distance as-is the chuck-3.

The holes I, 'l in bar *5 are spncedifmm the -'-chuck at distances such that :end portions of-a wire 'rOf given diameter to ice-tested will be :bent around in ."a particular form, as will he hereinaiter described "for testing according tothe method *of'tli-is invention.

The "wire twill ice supported "intermediate lts ends andsu'ch may be conveniently acc omplished by Jiorming' the top of table 2 of steel and providing magn'ets il, it, each marrying a member 9, which in iturn carriesrra :latemlly extending pin 5am. fl'lhe magnet may he fina'gnetically :engaged with the steel top of table 2 at desired points for the support of the wire on the laterally extending pins In, which will be arranged to support the wire in parallelism with the surface oi. "tablet As will now be appreciated, when the motor I is operated the wire I will be rotated about its axis and, being stressed in the form in which it is supported, will ultimately break the maxi- ;mum rbend-ingzstress :on the wire is in excess of the endurance ilimit 'oi-the material of the wire. In order to determine the-number of l-rotations :of the wire required to break it and the period of time during which it is.r0tated,- the circuit shown inEig-ure3 may be conyenientlyused.

In Figure 3 a circuit A carrying, for example, an alternating current 0160 cycles, ,i-rom any convenient source, is connected through an indicator lamp l2 and a transformer 18. For control of the circuit through the transformer and lampta manually operated "switch His pro-- vided. "The circuit "A is also connected to an electric clock-Hand the winding Hi "of motor 1 through relay contacts 43. Switches [5 and IB vare providedior independent control of the .clock on themotor shaf-ttisua'chuck 3 adapted to grip and motor.

A current of low value is set up by the transformer in a circuit including the wire 4 and relay coil 2|.

As will now be obvious, on the closing of switch II, by virtue of the current set up by the transformer in the circuit including the relay coil :21, the contacts l3 will be closed and if the switches l5 and I6 be closed the clock and motor will be operated. Operation of the'motor will effect r0- tation of the wire 4 and the clock will serve to measure the period during which the wire is rotated, from which, given the R. P. M. .of the motor the total number .of turns of the wire can be calculated.

.When the rwiretbreaks the circuit includin the relay coil 2-] willibe broken-and the relay contacts 13 will open, with the resultthat the motor and'clock will stop.

By virtue of the provision oi switches l5 and t6 a-the:motor and clock may the controlled independently when relay contacts are closed by the setting up of a current in the circuit including the relay coil 2| and the Wire 4. Thus, when the relay contacts are closed, the clock can be operated for setting without operation of the motor and rotation of the wire 4 and likewise, where desired, the motor can be operated without operation of the clock.

Since the current set up in the circuit including wire 4, will be of low value, in order to obtain good contact with the bar 5, the holes I therein may desirably be provided, as shown in Figure 4, with bushings 22, preferably of glass, opening at the rear of the bar 5 into a cup 23 containing mercury 24, into the end of which wire A penetrates and from which a lead 25 extendsfor connecting the wire into the circuit. The

bushing 22 will be of an inside diameter somewhat larger than the wire, but the clearance will be such as not to permit any substantial amount of mercury to pass from. the cup 23.

According to the method'of this invention, for the carrying out of which the above described apparatus is adaptable, a-length of wire of given diameter will be rotated, as in the rotating beam fatigue test, in a looped form, and having its ends supported at points where the bending movement of the loop becomes zero, leaving only a lateral force acting horizontally between the points of ent stresses. the apparatus above described may be constructed for the test of wire under difierent lae, additional length being allowed for entry into .the chuck and properly spaced hole 1 in bar 5.

The testing of any given wire set up according to this invention is then carried out by rotating it until it breaks, as in the usual rotating beam fatigue test, it being noted that the support afforded to the loop by the pins I 0 suppresses vibration, hence submersion in an oil bath is unnecessary. And it will be further noted that the holes 1, 1 in bar 5 need not accurately fit the wire so that if desired one hole size may be used with a range of wire diameters. a r

Generally speaking. a given wire under test'will break at the point of minimum radius of curvature where the stresses will be at maximum. However, by calculation convenient evaluation of an elf-center break is shown in the following table: V

support, and hence with the maximum stress, which may be in excess of the endurance limit of th material of the wire, at the point of minimum radius of curvature of the loop.

In order to obtain this condition, it has been found that a certain constant relationship exists between the vertical distance from the plane of the points of support of the ends of the wire and the height of the loop, i. e., the distance h, Figure 2, and the horizontal distance between the points of end support, 1. e., the distance C, Figure 2. As a consequence, given the diameter of a I wire and the bending stress under which it is to be tested, according to this invention the requisite distances C and h, the'required length of wire, the minimum radius of curvature and the lateral force at the points of end support of the loop can readily be obtained by application of the following formulae. Thus: c=1.19s h=0.835 C L=2.19 C'=2.82 Where E= Youngs modulus R .,,=0.4lE7dC d=Diarneter of wire C= Distance between points of support of loop h=Height of loop L=Length of wire between points of end support Minimum radius of curvature P= Bushing load or lateral force at the chuck s=Bending stress under which wire is to be tested Having determined the distances C and h, Figure 2, for the formation of a loop of proper form for wire of a, plurality of diameters under difier- The method and apparatus according to this invention will :be found to enable the necessary data to be obtained in a short time. and especially at the high stresses at which spring wire is usually tested.

What I claim and desire to protect by Letters Patent is:

1. The method of rotating beam fatigue testing wire which includes supporting at opposite points a loop of wire with the ends of the wire extending from the loop parallel to each other and of a form such that the distance between the points of support of the loop will equal where E is Youngs modulus, dis the diameter of the wire and s is a bending stress in excess of the endurance limit of the material of the Wire under which the wire is to be tested and such that the height of the loop is equal to 0.835 times the distance between the points of support of the loop and rotating the wire until it breaks.

2. An apparatus for subjecting a test wire of small diameter to fatigue testing, comprising a support, a chuck mounted for rotation on said support for holding one end of the wire. means for rotating said chuck, and a member on the support having a pluralityof predeterminedly spaced openings therein into either of which the other end of the wire may be extended for rotation and to form a loop of predetermined size, the axes of the openings being parallel with the axis of the chuck, whereby the ends of the wires extending from the loop are maintained parallel to each other.

3. An apparatus for subjecting a test wire of small diameter to fatigue testing, which com prises a base, a pair of supports mounted on said base and provided with apertures for the reception of the ends of a loop of wire and arranged in spaced relation, the axes of the apertures in said supports being in parallelism and the wire receiving ends of said apertures being in a plane normal to the axes of the apertures, one of said supports being constructed to permit the end of the wire to be spaced at varying distances from the other end to vary the size of the loop while maintaining the two ends parallel, and means mounted on said base and coaxial with one of said support apertures for rotating the wire forming the loop.

4. The method of testing wire which includes supporting a loop of wire at opposite points with the portions of the ends of the wire extending from the loop to said points parallel to each other, whereby only a lateral force tending to spread the points or support in a substantially straight line is exerted and the bending movement of the wire is zero at the points of support and the maximum stress on the wire falls at the point of minimum radius of curvature of the loop and rotating the wire so supported until the wire in the loop portion is broken.

PHILIP C. CLARKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Article, "New Test for Cable Wire, page 205 of 20 April 1936 issue, Scientific American. (A photostat copy is in class 73-100.) 

